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j. Soc. Cosmet. Chem., 43, 161-167 (May/June 1992) ServoMed evaporimeter: Precautions when evaluating the effect of skin care products on barrier function BOYCE M. MORRISON, JR., Gillette Research Institute, 401 ProJ•ssional Drive, Gaithersburg, MD 20879. Received January 17, 1992. Presented at the 16th IFSCC Congress, New York, October 1990. Synopsis The ServoMed evaporimeter has become a commonly used instrument in the laboratories of cosmetic scientists who are investigating the effects of skin care products on barrier function and on skin condition. The ServoMed evaporimeter measures transepidermal water loss (TEWL) by estimating the vapor pressure gradient of water immediately adjacent to the surface of the skin. This report shows that the response of the evaporimeter can be affected by the evaporation of certain volatile organic compounds. The effects of two humectants, propylene glycol and glycerol, on TEWL measurements were examined after application of materials to humans and to glass slides. The data indicate that the evaporimeter responds to the two materials in distinctly different ways: propylene glycol apparently increases the response, whereas glycerol does not. Small volatile organic molecules, such as propylene glycol, adsorb onto the polymeric surfaces of the probe, resulting in artificially high readings. Less volatile organics, i.e., glycerol, do not adsorb. Therefore, it is important that all materials and products present during measurements be tested to determine their adsorption characteristics and that the calibration of the evaporimeter be checked after exposure to products containing volatile organics. A waiting period of 2-3 hours after product application is suggested in order to eliminate (or reduce) interactions between the applied materials and the evapo- rimeter. INTRODUCTION The ServoMed EP1 evaporimeter (SeroMed AB, Stockholm, Sweden) has become a standard instrument in the laboratories of cosmetic scientists since it was introduced by Nilsson in 1977 (1). It measures transepidermal water loss (TEWL) and has been used to assess the effect of skin care products on skin condition and barrier function. Increases in TEWL have been attributed, in general, to a breakdown in the barrier properties of the skin. After removal of the stratum corneum via tape stripping, TEWL can increase by as much as a factor of thirty (2). When exposed to an irritant such as sodium lauryl sulfate, TEWL can increase by a factor of 3 to 50, depending on the exact concentration The present address of Boyce M. Morrison, Jr. is Colgate-Palmolive Company, 909 River Road, P.O. Box 1343, Piscataway, NJ 08855-1343. 161